Method of preparing nickel powder with large surface area



Patented Nov. 24, I953 METHOD OF PREPARING NICKEL POWDER WITH LARGE SURFACE AREA Nicholas J. De Lollis, Arlington, Va., assignor to the United States of America as represented by the Secretary of Commerce No Drawing. Application January 25, 1952, Serial No. 268,326

(Granted under Title 65)U. S. Code (1952),

2 Claims.

The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon in accordance with the provisions of the act of March 3, 1883, as amended (45 Stat. 467; 35 U. S. C. 45).

The present invention relates to the production of nickel powder and more particularly to a powder with a very large surface area. When nickel is used as a chemical, physical, or catalytic agent, it is sometimes desirable to have the metal in a finely divided porous state so that the surface area per gram is large. As an example, it is sometimes necessary to measure the quantity of heat produced when nickel is wet with certain liquids. The greater the surface area of the nickel the more heat is evolved and therefore the measurements are easier to obtain and more accurate. Nickel powders are also used in the hydrogenation of vegetable oils for the production of shortenings. At the present time the best of the commercially available nickel powders have surface areas of only 1 square meter per gram as measured by the nitrogen adsorption method. Other nickel powders have been produced with surface areas of 50 square meters per gram but these are not commercially available and have to be made up by the individual as desired. Also the production of these powders is not simple and involves some rather complex steps.

The object of this invention is to produce a nickel powder with a very large surface area.

In accordance with the present invention nickel oxalate is decomposed at a temperature well below the melting and sintering temperatures of the metal and below the melting point of the nickel salt. The volatile gases leaving the rigid structure of the nickel salt leave it in a very porous state resulting in a large surface area. Surface areas up to 54 square meters per gram have been obtained.

The procedure followed in producing the finely divided powder is as follows:

Nickel oxalate (NiC2O4'2I-I2O) is heated at 200 degrees centigrade in an oven until it loses all of its water of crystallization. This is checked by weighing before and after heating. The anhydrous salt is then put in a glass tube to which a stopcock is sealed. The tube is put in an oven controlled at 320 degrees centigrade degrees centigrade. The stopcock end sticks out of the oven and is attached to a vacuum system so that the decomposition proceeds in a vacuum.

This minimizes any chance for conversion to the oxide or carbonate and probably accelerates the decomposition.

Every twenty four hours the stopcock is closed. The tube is taken out of the oven, cooled to room temperature and weighed. When the weight loss shows that the decomposition is complete the heating is discontinued; actually ninety-nine percent complete is sufiicient. After the nickel has cooled to. room temperature while still in the vacuum, the powder is ready for use. If the powder is to be stored benzene or any inert gas or liquid is added to the nickel slowly so that the heating effect will be kept to a minimum. This is done without exposing the nickel to air. The nickel is stored in benzene to protect it from oxidation.

To prepare for use, the nickel benzene mixture is put into glass bulbs which are connected to a vacuum system. The bulbs are cooled in ice water while the benzene is taken off by evacuation so that the benzene does not boil off and thereby carry the nickel into the vacuum system. After the benzene has been removed, the evacuation is continued at the temperature at which decomposition takes place; 320 degrees centigrade. Higher temperatures result in loss of surface area due to sintering. The glass bulbs are sealed off when the pressure is about 1O" mm. of mercury.

Nickel powder prepared by this method has a surface area of 5a square meters per gram. Nickel prepared at .00- degrees centigrade has a surface area of 44 square meters per gram, indicating that the surface area is very sensitive to higher temperatures, and decomposition temperatures should be kept as low as possible to insure the reatest surface areas.

The nickel produced by this method is a very fine black powder. It is pyrophoric; that is, it glows with a red heat and throws off sparks when exposed to air. When immersed in liquids such as ethyl alcohol and benzene it evolves heat in the range of 0.1 to 0.2 calorie per square meter.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of my invention as defined in the appended claims.

I claim:

1. A process for preparing nickel powders with large surface areas which comprises the steps of heating nickel oxalate at 200 degrees centigrade until all the water of crystallization is driven off, thereby forming an anhydrous salt, and heating 3 the anhydrous salt in a vacuum at a temperature in the range of 310 degrees centigrade to 330 de grees centigrade until decomposition is 99 to 100 percent complete.

2. A process for preparing nickel powders with surface areas of 54 square meters per gram of powder comprising the steps of heating nickel oxalate at 200 degrees C. until all of the water of crystallization is driven off, thereby forming an anhydrous salt, and heating the anhydrous salt 10 in a vacuum at 320 degrees C. until decomposition is 99 to 100 per cent complete.

NICHOLAS J. DE LOLLIS.

References Cited in the file of this patent A Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 12, page 768, edited by Mellor, published in 1931 by Longmans, Green and 60., New York. 

1. A PROCESS FOR PREPARING NICKEL POWDERS WITH LARGE SURFACE AREAS WHICH COMPRISES THE STEPS OF HEATING NICKEL OXALATE AT 200 DEGREES CENTIGRADE UNTIL ALL THE WATER OF CRYSTALLIZATION IS DRIVEN OFF, THEREBY FORMING AN ANHYDROUS SALT, AND HEATING THE ANHYDROUS SALT IN A VACUUM AT A TEMPERATURE IN THE RANGE OF 310 DEGREES CENTIGRADE TO 330 DEGREES CENTIGRADE UNTIL DECOMPOSITION IS 99 TO 100 PERCENT COMPLETE. 